1. Field of the Invention
The present invention relates to bituminous roofing products such as asphalt-based roofing membranes, roofing shingles, and processes for making such roofing products.
2. Brief Description of the Prior Art
Asphalt-based roofing membranes are excellent waterproofing materials that have been extensively used in low-slope roofing systems to provide long-lasting and satisfactory roof coverings. Low-slope roofing systems are extensively used for commercial and industrial buildings. Examples of low-slope roofing systems are built-up roofs (BUR), modified bitumen roofs, and single-ply or membrane roofing systems. Asphalt-based roofing membranes are frequently used as waterproofing underlayment in low-rise roofing systems, as well as the uppermost or finish layer in built-up-roofs. The uppermost or “cap” sheet employed in membrane roofs often includes a layer of granular mineral material to protect the underlying roofing membrane.
Typically, bituminous roofing products are sheet goods that include a non-woven base or scrim formed of a fibrous material, such as a glass fiber mat. The base is coated with one or more layers of a bituminous material such as asphalt to provide water and weather resistance to the roofing product. Depending on the application, one side of the roofing product may be coated with mineral granules to provide durability, reflect heat and solar radiation, and to protect the bituminous binder from environmental degradation. Roofing granules can be embedded in the surface of such bituminous roofing products using conventional methods.
Mineral-surfaced asphalt shingles, such as those described in ASTM D225 or D3462, are generally used for steep-sloped roofs to provide water-shedding function while adding aesthetically pleasing appearance to the roofs. Conversely, roll goods such as asphalt-based roofing membranes are generally used for low-slope roofs. Pigment-coated mineral particles are commonly used as color granules in roofing applications to provide aesthetic as well as protective functions. Roofing granules are generally used in asphalt shingles or in roofing membranes to protect asphalt from harmful ultraviolet radiation.
Roofing products such as asphalt shingles and roll stock are typically composite articles including a non-woven glass fiber or felt web covered with a coating of water repellent bituminous material, and optionally surfaced with protective surfacing media. Surfacing media, such as inert mineral granules, fine sands, talc, limestone powder, calcium carbonate powder, or finely crushed rock powders, are typically used in roofing products to provide a tack-free surface for web-style manufacturing process, or the ability for packaging and storage. Some types of surfacing media, such as traditional roofing granules, can also provide UV protection to the covered asphalt binder and add aesthetic values to the end products. With the proper size and surface coverage of the roofing granules, it is reported that additional fire protection of the end products can be achieved. However, the resultant roofing products are known to have low solar reflectivity and hence will absorb significant solar heat especially through the infrared range of the solar spectrum. This phenomenon is increased as the granules covering the surface become dark in color. This is due in part to the rough surfaces created by typical roofing granules that can trap solar radiations and hence result in low solar reflectance. Although this phenomenon can be alleviated to a certain degree by reducing the granule size for a smoother surface, however, the benefit of increased fire resistance in end products would be greatly reduced. Also, other surfacing media are limited in providing high solar reflectance, adequate UV and fire protection to the end products without the aid of other ingredients, such as flame retardants added to the asphalt binder or the use of white protective coating.
Asphalt based roofing products have the challenge of meeting demanding fire resistance requirements set forth by national and international codes. One way in which fire resistance is improved is by adding fire retardant chemicals to the asphaltic materials themselves.
The fire resistance properties of roofing systems are typically measured using Underwriters' Laboratories 790 test method, Tests for Fire Resistance of Roof Covering Materials, which includes three test procedures, spread of flame, intermittent flame, and burning brand tests. This test employs a roof deck that slopes upward from the source of flame.
Laminated single-ply roofing membranes are known, such as those disclosed in U.S. Pat. Nos. 6,502,360; 5,456,785; 5,620,554; and 5,643,399. U.S. Pat. No. 6,296,912 discloses a roofing membrane having a fibrous layer on top for providing a secure surface for roof installation personnel.
Multilayer roofing membranes reinforced with polymeric materials are known. Such membranes are available, for example, faced with polyethylene film, or with mineral particles bonded to an underlying polyethylene film.
U.S. Pat. No. 4,218,502 discloses a moisture-resistant, intumescent fire retardant based on hydrated metal silicate coated with a protective coating comprising a metal salt with long-chain fatty acid. This fire retardant is dispersed within asphaltic coating material to form flame-retarded roofing products. U.S. Pat. No. 4,287,248 discloses a bituminized roofing sheet with improved flame resistance. The roofing sheet consists of a reinforced fleece, bitumen, and a metal foil placed on one face of the sheet. U.S. Pat. No. 5,000,999 discloses a bituminized roofing sheet having a metal foil applied to the bottom of the lower layer and optionally to the upper surface of the roofing sheet.
There is a continuing need for roofing materials that have improved resistance to fire while providing good weatherproofing characteristics.